1. Field of the Invention
The present invention relates to a mobile communication system which carries out packet communication, and a method of controlling the same.
2. Description of the Related Art
In recent years, a mobile communication system has been studied in which the Internet is accessed from a mobile terminal.
An example of such a mobile communication system is disclosed in a first reference, “3GPP2 P.S001 version 1.0 Wireless IP Network Standard, Dec. 10, 1999”. Here, the technique disclosed in the first reference will be simply described with reference to FIG. 1A.
As shown in FIG. 1A, the mobile communication system disclosed in this first reference is composed of a radio access network (RAN) 13, a core network (Core Network; CN) 15a, and the Internet 16. The radio access network RAN 13 includes a radio base station (Node B; NB) 11 with which a mobile terminal 10 communicates through a radio channel, and a radio channel control station (Radio Network Controller; RNC) 12 which controls the radio base station 11. The core network 15a is composed of a home agent (HA) 14a and a foreign agent (FA) 14b to control a call of the mobile terminal 10.
In the mobile communication system, the communication between the core network 15a and the Internet 16 is controlled based on mobile IP (mobile IP) which is discussed in IETF (Internet Engineering Task Force). The mobile IP is a mobile control system studied in IETF. For example, it is disclosed in the second reference, “IETF RFC 2002, C. E. Perkins, IPv4 Mobility Support, October 1996”.
To realize the control based on this mobile IP, the home agent (HA) 14a of the core network 15 is installed in a home domain of the mobile terminal 10. The home agent 14a once receives a packet signal transmitted from a communication correspondent node of the mobile terminal 10 to the mobile terminal and transfers the packet signal to the mobile terminal 10 through the foreign agent (FA) 14b. Also, the foreign agent FA 14b detects that mobile terminal 10 is moving into a domain managed by the foreign agent FA 14b, notifies that the mobile terminal 10 is moving into the domain managed by the foreign agent FA 14b, to the home agent 14a. 
On the other hand, communication between the foreign agent FA 14b of the core network 15a and the mobile terminal 10 is controlled based on channel switching connection. In the channel switching connection, a fixed band is previously allocated to each mobile terminal to carry out communication.
Also, another example of the mobile communication system is disclosed in the third reference, “3GPP TR23.923 version 1.0.0 Combined GSM and Mobile IP Mobility Handling in UMTS IP CN, Oct. 06, 1999”. Here, the technique disclosed in the third reference will be simply described with reference to FIG. 1B.
As shown by FIG. 1B, in case of the second reference, the communication of the Internet 16 is controlled based on the mobile IP. On the other hand, the communication between the core network (CN) 15b and the radio channel control station RNC 12 is controlled based on GTP (GPRS Tunneling Protocol) which is a mobile control system peculiar to the mobile communication system.
However, in the technique disclosed in the above-mentioned first reference, the channel switching connection is carried out. For this reason, a communication band is occupied even when the mobile terminal does not carry out the transmission and reception of data.
Also, in the technique disclosed in the above-mentioned second reference, in the core network, the control system peculiar to the mobile communication system is used. For this reason, the communications protocol is redundant so that the overhead of the communication increases and the network structure is limited.
In conjunction with the above description, a mobile radio communication network is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 4-373222). In this reference, the mobile radio communication network is composed of a plurality of radio base stations and a plurality of mobile stations, a PSTN network connected to a telephone, and a circuit control station which controls the whole network. A circuit connection unit connected to the radio base station, a PSTN connection unit connected to the PSTN network and a circuit control station are connected by a loop approach circuit.
Also, a mobile communication system is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 5-268150). In this reference, the mobile communication system is composed of a plurality of mobile stations (MS), a plurality of radio base stations (BS), a radio channel control station (CS) and a switching station. The radio base station is a counter station of the mobile station, and transmits and receives signals using a plurality of connection control channels and a plurality of communication channels, and has a function to relay the signals between the radio channel control station and the mobile station. The radio channel control station has a function to control the setting of the communication channels. The mobile station has a function to always or periodically monitor notice data transmitted on downstream of the connection control channel. The communication channel can be switched between speech communication or continuous data communication in a first use mode and time divisional multiple access communication of burst data in a second use mode. Data of the communication channel in the second use mode is added to the notice data. The communication channel in the second use mode has m time slots for one frame of upstream n time slots for one frame of downstream (m and n are positive integers). A data communication function (6,7) is added to insert in a predetermined time slot of downstream, data indicative of a use state of the other time slots of the same frame.
Also, a radio communication system is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 8-251229). In the radio communication system of this reference, when both or one of a speech signal for speech communication and a data signal for data communications is inputted, a transmission unit transmits the inputted signal as a radio signal. A receiving unit receives the speech signal and the data signal from the transmission unit to output them. The transmission unit is provided with a speech packet processing section, a data packet processing section, a speech/data control section and a transmission section. The speech packet processing section divides a speech existing portion of the speech signal in units of predetermined units to generate speech packets. The data packet processing section divides a data existing portion of the data signal in units of predetermined units to generate data packets. The speech/data control section determines a transmission order of the speech packets generated by the speech packet processing section and the data packets generated by the data packet processing section. The transmission section transmits the speech packets and the data packets to the reception apparatus in accordance with the transmission order determined by the speech/data control section. The reception apparatus is provided with a reception section, a speech/data identifying section, a speech signal reproducing section and a data signal reproducing section. The reception section receives the speech packets and the data packets from the transmission section. The speech/data identifying section identifies whether the received packet by the reception section is the speech packet or the data packet. The speech signal reproducing section reproduces a speech signal from the speech packets identified by the speech/data identifying section. The data signal reproducing section reproduces the data signal from the data packets identified by the speech/data identifying section.
Also, a radio access method and a radio communication system are disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-234286). In the radio access method of this reference, a radio station transmits a packet while a radio frequency is shared by a plurality of radio stations. At that time, the radio station can transmit the packet after it is confirmed that the radio frequency is not used over a priority station access time which can transmit a packet with priority without competition with the other stations and a random time which is selected from predetermined times. When receiving the packet a sending station, a receiving station can transmit a response packet, which notifies reception completion of the packet, to the sending station with priority after the priority station access time. In such a radio access method, in case to send back the response packet, the receiving station (1b) monitors whether the radio frequency is unused over the priority station access time and the random time, (1a) when a transmission wait data packet exists already in the receiving station. The receiving station transmits the transmission wait data packet, (1c) if the radio frequency is unused, and sends the response packet after the priority station access time after transmission completes of the transmission wait data packet. The receiving station (2b) monitors whether the radio frequency is unused over the priority station access time and the maximum time of the predetermined times after receiving the data packet, (2a) when any transmission wait data packet does not exist in the receiving station. The receiving station sends the response packet at once, (2c) if the radio frequency is unused. When the radio frequency is used during the monitor (1b) and (2b), the receiving station transmits the response packet after transmission completion of a data packet from one of the radio stations other than the receiving station and after the priority station access time passes.
Also, a radio data communication subsystem is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-275143). In this reference, the data communication system is composed of a radio interface and a digital network interface. The transmission and reception of data is carried out through the radio interface with a data communication terminal which is connected with a child terminal through a data communication unit. The transmission and reception of data is carried out through the digital network interface with a data communication terminal which is connected with a digital network through a data communication unit. The radio interface of a radio data communication apparatus has a function to establish a radio packet communication channel in accordance with a call connection procedure for the radio packet communication channel and to send and receive data using the radio packet communication channel, and a function to establish a radio communication channel in accordance with a call connection procedure for circuit switching and to send and receive data using the radio communication channel. Also, the digital network interface has a function to establish a digital network packet communication channel in accordance with a call connection procedure for the digital network packet communication channel and to carry out the transmission and reception of data using the digital network packet communication channel and a function to establish a digital network communication channel in accordance with a call connection procedure for circuit switching and to carry out the transmission and reception of data with using the digital network communication channel. When there is a call connection request, the radio interface establishes the radio packet communication channel in accordance with the call connection procedure for the radio packet communication channel. The digital network interface establishes the digital network packet communication channel in accordance with the call connection procedure for the digital network packet communication channel. The digital network interface automatically switches between the data communication using the radio packet communication channel and the data communication using the radio communication channel on the side of the radio interface, and between the data communication using the digital network packet communication channel and the data communication using the digital network communication channel on the side of the digital network interface based on whether an amount of data transmitted and received for a predetermined time interval between the data communication terminal which is connected with the child terminal through the data communication unit and the data communications terminal which is connected with the digital network through the data communication unit exceeds a predetermined threshold, the state of the radio communication channels, and the number of child terminals to be connected.